Photographs of the singer with the footballer have been widely published, and Simpson’s girlfriend said he “cheated” on her.
Stephanie Ward, the mother of Simpson’s daughter Skye-Lorena, said she is expecting their second child.
She told The Sun: “I have a baby on the way and a little girl who’s one-and-a-half. If he wants to leave that, then that’s up to him.
“But I won’t be here for him if he comes back. I don’t care any more. He’s made his bed, so he can lie in it.”
Speaking to her fans on Twitter, Contostavlos said: “I don’t want 2 get in2 a public war of words, but what is being written about me 2moro is absolutely not true.”
The star, who is currently on screen in The X Factor and rose to fame as part of N-Dubz, was pictured in Newcastle and Manchester with Simpson.